Hydrofluoric acid wastewater discharged in the manufacturing process of electronic components such as semiconductors and liquid crystals is diluted and difficult to reuse. Therefore, such wastewater is conventionally treated by a method comprising neutralizing the hydrofluoric acid with slaked lime (calcium hydroxide) to form insoluble calcium fluoride, precipitating the calcium fluoride together with calcium hydroxide and separating the precipitate as a sludge from the wastewater.
However, this method has a problem in that precipitation and dehydration require an excessively large equipment space. Furthermore, the necessity of supplying an excess of calcium hydroxide results in a large amount of sludge, so that massive amounts of waste remain even after dehydration. In addition, since 15 to 20 ppm of fluorine remains in the treated water, there is still room for improvement with regard to water quality.
In this connection, Japanese Unexamined Patent Publication No. 271785/1997 describes a hydrofluoric acid wastewater treatment method comprising adding an aqueous alkaline solution such as aqueous caustic soda solution or aqueous caustic potash solution to hydrofluoric acid wastewater, followed by concentration by evaporation to produce distilled water.